<p>
  <%= label_tag(:name, "Name") %>
  <%= f.text_field :name %>
</p>
<p>
  <% sex_array = { "男" => '1', "女" => '2'} %>
  <%= label_tag(:sex_id, "Sex") %>
  <%= f.select :sex_id, sex_array %>
</p>
<p>  
  <%= label_tag(:banji_id, "Banji") %>
  <%= collection_select(:student, :banji_id, Banji.all, :id, :name) %>
</p>